This invention relates to detectors for a.m. receivers and more particularly to the use of average detectors in place of the conventional peak detectors or in conjunction therewith.
When interference is present in a.m. receivers in the form of an off-frequency a.m. signal, somewhat weaker than the desired signal, three kinds of interference will appear in the detector output. The strongest will be the beat between the two carrier frequencies. This "carrier squeal" may or may not be important, depending upon whether it is within the audio band or above it. The second strongest will be the demodulation of the sidebands of the weaker signal with the carrier of the stronger. Since all the frequencies are wrong, this is generally not intelligible and is called "monkey chatter". Third will be the demodulation of these sidebands with their own carrier. Since this will be intelligible, it may cause more real interference with the intelligibility of the desired message.
The interfering signal will cause a carrier beat which will be modulated with the modulation of the interfering signal plus that of the desired signal. The peak detector of a conventional a.m. receiver will follow this modulation, thus, providing the intelligible intereference to the listener.
Conversely, in some situations (called conferencing) the listener desires to hear off-frequency signals, in which case one wishes to enhance the effect described above and reduce the volume of the output due to the strongest signal.